That demo/final comparison really says it all. They've clearly pissed away so much time developing their own IP, that the time has come where they couldn't delay this anymore so it's just been patched together & thrown out of the door.
Rather than optimising & polishing the game up, any graphical features that have hit the frame rate have just been removed completely, leaving a rough looking, glitchy mess. It's like a playable alpha masquerading as a full game.